The present invention generally relates to medical devices and methods for baroreflex activation. Specifically, the present invention relates to devices and methods for externally activating the baroreflex system before implanting a baroreflex activation device.
Cardiovascular disease is a major contributor to patient illness and mortality. It also is a primary driver of health care expenditure, costing more than $326 billion each year in the United States. Hypertension, or high blood pressure, is a major cardiovascular disorder that is estimated to affect over 50 million people in the United Sates alone. Of those with hypertension, it is reported that fewer than 30% have their blood pressure under control. Hypertension is a leading cause of heart failure and stroke. It is the primary cause of death in over 42,000 patients per year and is listed as a primary or contributing cause of death in over 200,000 patients per year in the U.S. Accordingly, hypertension is a serious health problem demanding significant research and development for the treatment thereof.
Hypertension occurs when the body's smaller blood vessels (arterioles) constrict, causing an increase in blood pressure. Because the blood vessels constrict, the heart must work harder to maintain blood flow at the higher pressures. Although the body may tolerate short periods of increased blood pressure, sustained hypertension may eventually result in damage to multiple body organs, including the kidneys, brain, eyes and other tissues, causing a variety of maladies associated therewith. The elevated blood pressure may also damage the lining of the blood vessels, accelerating the process of atherosclerosis and increasing the likelihood that a blood clot may develop. This could lead to a heart attack and/or stroke. Sustained high blood pressure may eventually result in an enlarged and damaged heart (hypertrophy), which may lead to heart failure.
Heart failure is the final common expression of a variety of cardiovascular disorders, including ischemic heart disease. It is characterized by an inability of the heart to pump enough blood to meet the body's needs and results in fatigue, reduced exercise capacity and poor survival. It is estimated that approximately 5,000,000 people in the United States suffer from heart failure, directly leading to 39,000 deaths per year and contributing to another 225,000 deaths per year. It is also estimated that greater than 400,000 new cases of heart failure are diagnosed each year. Heart failure accounts for over 900,000 hospital admissions annually, and is the most common discharge diagnosis in patients over the age of 65 years. It has been reported that the cost of treating heart failure in the United States exceeds $20 billion annually. Accordingly, heart failure is also a serious health problem demanding significant research and development for the treatment and/or management thereof.
Heart failure results in the activation of a number of body systems to compensate for the heart's inability to pump sufficient blood. Many of these responses are mediated by an increase in the level of activation of the sympathetic nervous system, as well as by activation of multiple other neurohormonal responses. Generally speaking, this sympathetic nervous system activation signals the heart to increase heart rate and force of contraction to increase the cardiac output; it signals the kidneys to expand the blood volume by retaining sodium and water; and it signals the arterioles to constrict to elevate the blood pressure. The cardiac, renal and vascular responses increase the workload of the heart, further accelerating myocardial damage and exacerbating the heart failure state. Accordingly, it is desirable to reduce the level of sympathetic nervous system activation in order to stop or at least minimize this vicious cycle and thereby treat or manage the heart failure.
A number of drug treatments have been proposed for the management of hypertension, heart failure and other cardiovascular disorders. These include vasodilators to reduce the blood pressure and ease the workload of the heart, diuretics to reduce fluid overload, inhibitors and blocking agents of the body's neurohormonal responses, and other medicaments.
Various surgical procedures have also been proposed for these maladies. For example, heart transplantation has been proposed for patients who suffer from severe, refractory heart failure. Alternatively, an implantable medical device such as a ventricular assist device (VAD) may be implanted in the chest to increase the pumping action of the heart. Alternatively, an intra-aortic balloon pump (IABP) may be used for maintaining heart function for short periods of time, but typically no longer than one month. Other surgical procedures are available as well.
It has been known for decades that the wall of the carotid sinus, a structure at the bifurcation of the common carotid arteries, contains stretch receptors (baroreceptors) that are sensitive to blood pressure. These receptors send signals via the carotid sinus nerve to the brain, which in turn regulates the cardiovascular system to maintain normal blood pressure (the baroreflex), in part through modulation of the autonomic nervous system. Electrical stimulation of the carotid sinus nerve (baropacing) has previously been proposed for therapeutic purposes. For example, U.S. Pat. No. 6,073,048 to Kieval et al., the full disclosure of which is incorporated herein by reference, discloses a system and method for stimulating the carotid sinus nerve based on various cardiovascular and pulmonary parameters.
Although each of these alternative approaches is beneficial in some ways, each of the therapies has its own disadvantages. For example, drug therapy is often incompletely effective. Some patients may be unresponsive (refractory) to medical therapy. Drugs often have unwanted side effects and may need to be given in complex regimens. These and other factors contribute to poor patient compliance with medical therapy. Drug therapy may also be expensive, adding to the health care costs associated with these disorders. Likewise, surgical approaches are very costly, may be associated with significant patient morbidity and mortality and may not alter the natural history of the disease. Accordingly, there continues to be a substantial and long felt need for new devices and methods for treating and/or managing high blood pressure, heart failure and their associated cardiovascular and nervous system disorders.
U.S. Pat. No. 6,522,926, assigned to the assignee of the present application and incorporated herein fully by reference, describes a number of systems and methods intended to activate the baroreflex system, typically by providing activation at or near one or more baroreceptors in the carotid sinus and elsewhere. Numerous specific approaches are described, including the use of coil electrodes placed over the exterior of the carotid sinus near the carotid bifurcation. U.S. patent application Ser. No. 10/402,911, assigned to the assignee of the present application and incorporated herein fully by reference, describes improved systems and methods for baroreflex activation to provide cardiovascular reflex control. U.S. patent application Ser. No. 10/402,393, assigned to the assignee of the present application and incorporated herein fully by reference, describes improved systems and methods for baroreflex activation for cardiovascular reflex control via coupled electrodes.
Other devices, methods and systems for baroreflex activation are described in U.S. patent application Ser. Nos. 09/702,089, 09/963,991, 09/964,079, 09/963,777, 10/284,063, 10/453,678, 60/505,121 and 60/513,642, all of which are assigned to the present assignee and all of which are hereby incorporated by reference. Some of these devices and methods, for example, use baroreflex activation for such purposes as epilepsy control (60/505,121) and pain control and sedation (60/513,642). In using these and other systems and methods for activating baroreceptors and/or structures in the area of baroreceptors such as nerve fibers connected to baroreceptors, carotid sinus nerves and the like, an implantable stimulation/activation device is typically placed in the patient. Currently available systems and methods, however, do not provide a way to test the efficacy of a baroreflex activation implant before it is implanted. Current systems also do not provide a way to determine where an implant should be placed in a patient, such as whether a 2-sided or 1-sided device should be implanted in a given patient's neck, and if 1-sided, then on which side.
Devices and methods for externally stimulating baroreceptors to monitor and control a patient's blood pressure are described in U.S. Pat. Nos. 6,050,952 and 5,727,558 to Hakki et al., the full disclosures of which are incorporated fully herein by reference. These devices and methods, however, are designed only for therapeutic use and do not provide for external baroreflex activation to assess patient response, help a physician choose a location in the patient's body for placing the implant, or the like. Thus, currently available baroreflex activation treatments generally involve attaching cumbersome external devices to a patient or implanting an implantable device without knowing beforehand whether it will work for a given patient.
Therefore, a need exists for devices and methods for evaluating a patient response to baroreflex activation before implanting an activation device in the patient. Ideally, such devices and methods would be non-invasive, external to the patient, or as minimally invasive as possible and would help determine whether a patient will have a desired response to an implantable baroreflex activation device. Also ideally, such devices and methods would help a physician decide where to implant a baroreflex activation device in a patient. It would also be ideal if such devices could be used with or incorporated into other implantable devices, such as cardiac pacemakers (including biventricular pacemakers), cardiac defibrillators or the like. At least some of these objectives will be met by the present invention.